As one answerer stated Anne McCaffrey is high on the list and yes her characters due come alive, so much so that you begin to care about them. Her Pern series stands as a classic but you should also read her books prior to the time she got into fantasy .
Of course Robert Heinlein who understood the dark and positives sides of humans and what really makes them tick.
Ayn Rand who's fact and fiction place her miles above most writers and she too understands what makes people tick. As a single writer who has impacted how people look at the world, she has to be in the top five. Her books "Atlas Shrugged" and the "Fountainhead" still, after many reads run chills down my back.
Shelby Foote is a writer who is the ideal of what a writer should be. His 20 year work (the Civil War) is a master piece of historical research and translation into language not only understandable but words representative of the human soul.
Of course there are the classical writers.
Who can exceed Alexander Dumas (the Senior) with such as the "The Man in the Iron Mask" or "The Count of Monte Cristo'.
Sir Conan Doyle with his "Adventures of Sherlock Holmes" or The White Company" must be on the list.
Isaac D'Israeli and his "Curiosities of Literature" should be a must read for everyone.
In the area of literature for young people there is a very special writer (artist) named Holland C. Holland. His books such as "Minn of the Mississippi" and "Paddle to the Sea" are only exceeded by his "Sea Bird."
Sadly, any list of worthy authors is only exceeded by the legions of writers who can't hold your interest past the first paragraph.